Lithium ion separator and method for manufacturing the same and method for manufacturing lithium ion battery

Abstract

The present disclosure provides a lithium ion diaphragm, a preparation method thereof and a preparation method of a lithium ion battery. The preparation method of the lithium ion diaphragm comprises the following steps: preparing an oily positive electrode coating slurry with butanone as a solvent, and adding an aerogel additive to the oily positive electrode coating slurry; preparing an aqueous negative electrode coating slurry with ethanol as a solvent, and adding an aerogel additive to the aqueous negative electrode coating slurry; coating the oily positive electrode coating slurry and the aqueous negative electrode coating on both sides of a base film respectively to obtain a lithium ion diaphragm with the oily positive electrode coating, the base film and the aqueous negative electrode coating arranged in sequence. The oily positive electrode coating and the aqueous negative electrode coating are added with the aerogel additive, which improves the infiltration effect of the electrolyte and the high-temperature heat shrinkage resistance. The oily positive electrode coating slurry adopts an oily system, which improves the adhesion of the oily positive electrode coating and the positive electrode sheet. The aqueous negative electrode coating slurry adopts a hydrophilic system, which improves the adhesion of the aqueous negative electrode coating and the negative electrode sheet.

Description

Technical Field

[0001] This disclosure relates to the technical field of lithium battery production, and in particular to a lithium-ion separator, a method for preparing the same, and a method for preparing a lithium-ion battery. Background Technology

[0002] To improve safety and electrochemical performance, the separators used in lithium-ion batteries are often coated using coating techniques. For example, for PE separators, common coatings include electrodeless ceramic coating, water-based PVDF coating, oil-based PVDF coating, and oil-based aramid coating.

[0003] In the production of lithium-ion battery cells, PVDF-coated separators require a hot-pressing process with the electrodes. PVDF bonds the electrodes to the separator, eliminating air from internal gaps, increasing cell rigidity, and maintaining uniform cell thickness. After the cells are wound or stacked and packaged, electrolyte is injected. During the hot-pressing process, poor adhesion between the separator and electrodes can leave gaps, residual gas, and separator wrinkles, leading to uneven distribution of internal resistance. This can cause localized overcharging or over-discharging during battery cycling, ultimately affecting battery consistency and cycle stability.

[0004] For example, prior art document CN201610853861.3 discloses a hydrophobic silica aerogel composite separator for lithium-ion batteries. This separator is a conventional separator with a hydrophobic silica aerogel coating on the surface of different thicknesses. It uses lightweight, heat-resistant silica aerogel with good wettability to organic electrolytes as the coating material, which greatly improves the heat resistance, wettability, and electrochemical performance of the polyolefin separator without increasing the separator's mass. However, this composite separator fails to solve the problem of inconsistent adhesion between the separator and the positive and negative electrodes, easily causing wrinkles in the separator and affecting battery consistency. Furthermore, the high-boiling-point solvent system makes the separator difficult to dry.

[0005] For example, prior art document CN202210532816.3 discloses an aerogel lithium-ion separator and its preparation method, including a base layer, which is a non-woven fabric, and an aerogel layer coated on at least one side of the base layer. The aerogel layer is composed of the following raw materials in parts by weight: 10-20 parts aerogel particles, 0.3-1 parts activator, 2-5 parts binder, and 40-50 parts deionized water. The aerogel lithium-ion separator has a thickness of up to 16 micrometers or even thinner, a porosity of over 60%, a pore size of 0.01-0.1 μm, and an areal density of 5 g / m². Aerogel battery membranes have good air permeability, high liquid absorption rate, low shrinkage rate, and high strength. However, this aerogel lithium-ion separator fails to solve the problem of adhesion differences between the separator and the positive and negative electrode sheets, which easily leads to wrinkles in the separator and affects the consistency of the battery. Summary of the Invention

[0006] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a lithium-ion separator with good adhesion to the electrode, improved electrolyte wetting effect and high-temperature heat shrinkage resistance, as well as a method for preparing the same and a method for preparing a lithium-ion battery.

[0007] The purpose of this disclosure is achieved through the following technical solution:

[0008] A method for preparing a lithium-ion separator includes the following steps:

[0009] An oily positive electrode coating slurry is prepared, wherein the oily positive electrode coating slurry contains an aerogel additive, and the solvent of the oily positive electrode coating slurry is methyl ethyl ketone (MEK).

[0010] An aqueous negative electrode coating slurry is prepared, wherein the aqueous negative electrode coating slurry contains an aerogel additive, and the solvent of the aqueous negative electrode coating slurry is ethanol;

[0011] The oily positive electrode coating slurry is coated on one side of the base membrane, and the watery negative electrode coating slurry is coated on the other side of the base membrane to obtain a transition-coated separator.

[0012] The transition-coated separator is dried to remove methyl ethyl ketone (MEK) and ethanol, thereby obtaining a lithium-ion separator with an oily positive electrode coating, a base film, and an aqueous negative electrode coating arranged in sequence.

[0013] In one embodiment, the temperature for drying the transition-coated diaphragm is 30°C-60°C, and the drying time is 0.5h-3h.

[0014] In one embodiment, the preparation of the oily positive electrode coating slurry includes the following steps:

[0015] The positive electrode coating binder is added to methyl ethyl ketone (MEK), and then the positive electrode coating dispersant is added and stirred and dispersed for 60 min-120 min to obtain the positive electrode intermediate slurry.

[0016] The positive electrode intermediate slurry is added with an aerogel additive and stirred and dispersed for 120-150 minutes to obtain an oily positive electrode coating slurry.

[0017] The oily positive electrode coating slurry comprises the following components by weight:

[0018] Positive electrode coating binder: 15%-30%;

[0019] Butyl ketone: 44.5%-79.5%;

[0020] Positive electrode coating dispersant: 0.5%;

[0021] Aerogel additives: 5%-25%.

[0022] In one embodiment, the positive electrode coating binder is at least one of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); the positive electrode coating dispersant is at least one of polyethylene glycol, hexadecylbenzene sulfonic acid, and modified polyacrylic acid.

[0023] In one embodiment, the preparation of the aqueous negative electrode coating slurry includes the following steps:

[0024] Add the negative electrode binder and thickener to ethanol, then add the negative electrode coating dispersant, and grind and disperse for 60 min-120 min to obtain the negative electrode intermediate slurry;

[0025] Aerogel additives are added to the negative electrode intermediate slurry and stirred and dispersed for 120-150 minutes to obtain an aqueous negative electrode coating slurry.

[0026] The aqueous negative electrode coating slurry comprises the following components by mass:

[0027] Negative electrode binder: 10%-20%;

[0028] Thickener: 5%-10%;

[0029] Ethanol: 45%-79.5%;

[0030] Negative electrode coating dispersant: 0.5%;

[0031] Aerogel additives: 5%-25%.

[0032] In one embodiment, the negative electrode binder is modified polyvinylidene fluoride; the negative electrode coating dispersant is at least one of polyethylene glycol, hexadecylbenzene sulfonic acid, and modified polyacrylic acid.

[0033] In one embodiment, the aerogel additive includes organic aerogels and inorganic aerogels, wherein the inorganic aerogel is at least one of SiO2 aerogel and Al2O3 aerogel; and the organic aerogel is at least one of polyurea aerogel and polyimide aerogel.

[0034] In one embodiment, the thickness of the base film is 5μm-20μm, the thickness of the oily positive electrode coating is 1μm-5μm, and the thickness of the watery negative electrode coating is 1μm-5μm.

[0035] A lithium-ion separator is prepared using the lithium-ion separator preparation method described herein.

[0036] A method for preparing a lithium-ion battery includes obtaining a lithium-ion separator using the method described above.

[0037] A positive electrode sheet, a lithium-ion separator, and a negative electrode sheet are wound together to form a core, and the core is hot-pressed to obtain a battery cell.

[0038] The hot-pressed battery cells are installed in the battery casing, and then liquid-filled formation is performed to obtain the lithium-ion battery.

[0039] Compared with the prior art, this disclosure has at least the following advantages:

[0040] 1. The above-mentioned method for preparing lithium-ion separators utilizes the porous network structure of aerogel additives to create a large number of pores between the oily positive electrode coating and the watery negative electrode coating, thereby improving the wetting effect of the electrolyte. The porous network structure of the aerogel additives also improves the high-temperature thermal shrinkage resistance of the lithium-ion separator and reduces the internal resistance of the battery.

[0041] 2. The oil-based positive electrode coating slurry uses an oil-based solvent. The oil-based positive electrode coating slurry is similar to the oil-based system of the positive electrode coating, which improves the adhesion performance between the oil-based positive electrode coating and the positive electrode. The water-based negative electrode coating slurry uses a water-based solvent coating. The water-based negative electrode coating slurry is similar to the water-based system of the negative electrode coating, which improves the adhesion performance between the water-based negative electrode coating and the negative electrode. This avoids the presence of gaps between the lithium-ion separator and the positive and negative electrodes, which would cause wrinkles in the lithium-ion separator. As a result, the lithium battery produced has better consistency and cycle stability.

[0042] 3. The oil-based positive electrode coating slurry uses methyl ethyl ketone (MEK) as the solvent, while the water-based negative electrode coating slurry uses ethanol. Both MEK and ethanol are low-boiling-point solvents, which makes the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry easy to volatilize during the baking process, avoiding solvent residue on the lithium-ion separator. The boiling points of MEK and ethanol are close, which makes the drying time of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry similar, thereby making the formed lithium-ion separator more uniform and resulting in better consistency of the battery made from the lithium-ion separator. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 The diagram shows the steps of the method for preparing the lithium-ion separator in this embodiment. Detailed Implementation

[0045] To facilitate understanding of this disclosure, a more complete description will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the present disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure.

[0046] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0048] To better understand the technical solutions and beneficial effects of this disclosure, the following detailed description is provided in conjunction with specific embodiments:

[0049] This invention relates to a method for preparing a lithium-ion separator. In one embodiment, the method includes the following steps: preparing an oily positive electrode coating slurry, wherein the oily positive electrode coating slurry contains an aerogel additive, and the solvent of the oily positive electrode coating slurry is methyl ethyl ketone (MEK); preparing an aqueous negative electrode coating slurry, wherein the aqueous negative electrode coating slurry contains an aerogel additive, and the solvent of the aqueous negative electrode coating slurry is ethanol; coating one side of a base membrane with the oily positive electrode coating slurry and the other side of the aqueous negative electrode coating slurry to obtain a transition-coated separator; drying the transition-coated separator to remove MEK and ethanol, thereby obtaining a lithium-ion separator with an oily positive electrode coating, a base membrane, and an aqueous negative electrode coating sequentially disposed.

[0050] Please see Figure 1 The method for preparing a lithium-ion separator according to an embodiment of the present invention includes the following steps:

[0051] S101 Prepares an oily positive electrode coating slurry, wherein the oily positive electrode coating slurry contains an aerogel additive, and the solvent of the oily positive electrode coating slurry is methyl ethyl ketone (MEK). In this embodiment, the aerogel additive can increase the membrane's resistance to high-temperature thermal shrinkage and improve the absorption of electrolyte in the oily positive electrode coating.

[0052] S103 prepares an aqueous negative electrode coating slurry, wherein the aqueous negative electrode coating slurry contains inorganic aerogel and organic aerogel, and the solvent of the aqueous negative electrode coating slurry is ethanol. In this embodiment, the aerogel additive can increase the membrane's resistance to high-temperature thermal shrinkage and improve the absorption of electrolyte in the aqueous negative electrode coating.

[0053] S105 The oily positive electrode coating slurry is coated on one side of the base film, and the aqueous negative electrode coating slurry is coated on the other side to obtain a transition-coated separator. In this embodiment, the oily positive electrode coating slurry is located on the side opposite to the positive electrode sheet, and the aqueous negative electrode coating slurry is located on the side opposite to the negative electrode sheet, so that the oily positive electrode coating of the lithium-ion separator is bonded to the positive electrode sheet, and the aqueous negative electrode coating is bonded to the negative electrode sheet.

[0054] S107 The transition-coated separator is dried to remove methyl ethyl ketone (MEK) and ethanol, resulting in a lithium-ion separator with an oily positive electrode coating, a base film, and an aqueous negative electrode coating sequentially arranged. In this embodiment, during the separator drying process, solvents with lower boiling points evaporate first, while slurries with higher boiling points evaporate more slowly. When the slurry on one side of the base film is dry, the slurry on the other side is not completely dry, resulting in different degrees of dryness and wetness of the lithium-ion separator, thus leaving solvent residue in the lithium-ion separator. The boiling point of methyl ethyl ketone (MEK) is 79℃, and that of ethanol is 78℃. Both MEK and ethanol are low-boiling-point solvents, which makes it easy for the solvents in the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry to evaporate completely. Moreover, the boiling points of MEK and ethanol are less than 10℃ apart, which makes the low-temperature drying speeds of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry similar. This results in the same drying time for the oil-based positive electrode coating and the water-based positive electrode coating, leading to a more uniform lithium-ion separator.

[0055] The aforementioned method for preparing lithium-ion separators utilizes a porous network structure of aerogel additives, creating numerous pores between the oil-based positive electrode coating and the water-based negative electrode coating. This enhances the wetting effect of the electrolyte. The porous network structure of the aerogel additives also improves the high-temperature thermal shrinkage resistance of the lithium-ion separator, reducing the battery's internal resistance. The oil-based positive electrode coating slurry uses an oil-based solvent, similar to the oil-based system of the positive electrode coating, thus improving the adhesion between the oil-based positive electrode coating and the positive electrode sheet. Similarly, the water-based negative electrode coating slurry uses a water-based solvent coating, similar to the water-based system of the negative electrode coating, further improving the adhesion between the water-based negative electrode coating and the negative electrode sheet. The bonding performance prevents gaps between the lithium-ion separator and the positive and negative electrode sheets, thus avoiding wrinkles in the lithium-ion separator and resulting in better consistency and cycle stability of the manufactured lithium battery. The oil-based positive electrode coating slurry uses methyl ethyl ketone (MEK) as the solvent, and the water-based negative electrode coating slurry uses ethanol as the solvent. Both MEK and ethanol are low-boiling-point solvents, which makes the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry easy to volatilize during the baking process, avoiding solvent residue on the lithium-ion separator. The boiling points of MEK and ethanol are similar, which makes the drying time of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry similar, thus making the formed lithium-ion separator more uniform and resulting in better consistency of the battery made from the lithium-ion separator.

[0056] In one embodiment, the drying temperature of the transition-coated separator is 30℃-60℃, and the drying time is 0.5h-3h. In this embodiment, when the drying temperature of the transition separator is too high, the solvent evaporation rate of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry is faster. When the solvent evaporation rate is too fast, it is easy to cause unevenness of the coating surface, resulting in uneven stress on the obtained lithium-ion separator. This leads to wrinkles when the lithium-ion separator is wound with the electrode sheet. Both methyl ethyl ketone (MEK) and ethanol are low-boiling-point solvents. During the baking process, MEK and ethanol are also easy to evaporate at low baking temperatures. The original separator drying process requires more than 8 hours. The drying time of the transition-coated separator is reduced to 0.5h-3h, which reduces the drying time of the transition-coated separator and improves the production speed of the lithium-ion separator.

[0057] Furthermore, a double-sided coating device is used to simultaneously coat both sides of the base membrane. The double-sided coating device includes two dies respectively set on both sides of the base membrane. The oil-based positive electrode coating slurry and the water-based negative electrode coating slurry are coated on both sides of the base membrane through the two dies to obtain a transition-coated separator. The transition-coated separator is then dried in a floating drying oven to dry the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry on both sides of the base membrane, so that the oil-based positive electrode coating and the water-based negative electrode coating are formed on both sides of the transition-coated separator, thereby making the uniformity of the dried oil-based positive electrode coating and the water-based negative electrode coating better and accelerating the production efficiency of lithium-ion separators.

[0058] In one embodiment, the base film is a composite coating of PE and PP. In this embodiment, the composite coating of PE and PP is more heat-resistant than PP; PP has a higher melting point and closed-cell temperature than PE. The composite coating of PE and PP gives the base film the advantages of low closed-cell temperature and high melting temperature, while also possessing high oxidation resistance and puncture resistance.

[0059] In one embodiment, the preparation of the oily positive electrode coating slurry includes the following steps:

[0060] The positive electrode coating binder is added to methyl ethyl ketone (MEK), and then the positive electrode coating dispersant is added and stirred and dispersed for 60 min-120 min to obtain the positive electrode intermediate slurry.

[0061] The positive electrode intermediate slurry is added with an aerogel additive and stirred and dispersed for 120-150 minutes to obtain an oily positive electrode coating slurry.

[0062] The oily positive electrode coating slurry comprises the following components by weight:

[0063] Positive electrode coating binder: 15%-30%;

[0064] Butyl ketone: 44.5%-79.5%;

[0065] Positive electrode coating dispersant: 0.5%;

[0066] Aerogel additives: 5%-25%.

[0067] In this embodiment, the positive electrode coating binder is mixed evenly with methyl ethyl ketone (MEK), and 5%-25% aerogel additive is added to ensure that the aerogel additive is uniformly distributed within the prepared oily positive electrode coating slurry. When the aerogel content is less than 5%, the porosity of the aerogel additive is low, resulting in a decreased electrolyte absorption effect. When the aerogel additive content is greater than 25%, the porosity of the aerogel additive is high, but the aerogel additive can affect the adhesion performance of the oily positive electrode coating. The porous network structure of the aerogel additive gives it high porosity, resulting in a large number of pores within the oily positive electrode coating formed after the oily positive electrode coating slurry dries. This allows the oily positive electrode coating to accommodate more electrolyte. The porous network structure of the aerogel additive also improves the wettability between the electrolyte and the oily positive electrode coating. The low thermal conductivity of the aerogel additive improves the high-temperature heat shrinkage resistance of the oily positive electrode coating formed after the oily positive electrode coating slurry dries.

[0068] In one embodiment, the positive electrode coating binder is at least one of polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); the positive electrode coating dispersant is at least one of polyethylene glycol, hexadecylbenzene sulfonic acid, and modified polyacrylic acid. In this embodiment, when the mixing rate of PVDF or PVDF-HFP with methyl ethyl ketone (MEK) is slow, the MEK is preheated. The oily positive electrode coating formed by PVDF or PVDF-HFP is similar to the oily system of the positive electrode material in the positive electrode sheet, resulting in stronger adhesion between PVDF or PVDF-HFP and the positive electrode sheet. When polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is hot-pressed, PVDF or PVDF-HFP can fully bond inorganic aerogel and organic aerogel together and tightly connect with lithium-ion membrane.

[0069] In one embodiment, the preparation of the aqueous negative electrode coating slurry includes the following steps:

[0070] Add the negative electrode binder and thickener to ethanol, then add the negative electrode coating dispersant, and grind and disperse for 60 min-120 min to obtain the negative electrode intermediate slurry;

[0071] Aerogel additives are added to the negative electrode intermediate slurry and stirred and dispersed for 120-150 minutes to obtain an aqueous negative electrode coating slurry.

[0072] The aqueous negative electrode coating slurry comprises the following components by mass:

[0073] Negative electrode binder: 10%-20%;

[0074] Thickener: 5%-10%;

[0075] Ethanol: 45%-79.5%;

[0076] Negative electrode coating dispersant: 0.5%;

[0077] Aerogel additives: 5%-25%.

[0078] In this embodiment, when the aerogel content is less than 5%, the porosity of the aerogel additive is low, resulting in a decreased electrolyte absorption effect. When the aerogel additive content is greater than 25%, the porosity of the aerogel additive is high, but the aerogel additive affects the adhesion performance of the waterborne negative electrode coating. The adhesion performance of the waterborne negative electrode coating is relatively poor, and the aerogel additive has a significant impact on the adhesion performance of the waterborne negative electrode coating. Adding 5%-25% aerogel additive to the intermediate negative electrode slurry, the porous network structure of the aerogel additive gives it high porosity, resulting in a large number of pores in the aqueous negative electrode coating formed after drying. This allows the aqueous negative electrode coating to hold more electrolyte. The porous network structure of the aerogel additive also improves the wettability between the electrolyte and the aqueous negative electrode coating. The low thermal conductivity of the aerogel additive improves the high-temperature heat shrinkage resistance of the aqueous negative electrode coating formed after drying. Since both the aqueous negative electrode coating and the negative electrode material of the negative electrode sheet are aqueous systems, the adhesion between the aqueous negative electrode coating and the negative electrode sheet is improved. Because the intermediate negative electrode slurry is aqueous, the negative electrode binder needs to be evenly dispersed in the aqueous solvent ethanol to form a stable suspension or emulsion state of the aqueous negative electrode coating slurry. The negative electrode binder needs to be fully ground and dispersed using grinding equipment. By continuously grinding the intermediate negative electrode slurry with grinding equipment, the negative electrode binder in the intermediate negative electrode slurry is evenly dispersed. Ethyl cellulose can adjust the viscosity of the negative electrode coating slurry, so that the prepared water-based negative electrode coating slurry is easy to coat, thereby making the obtained water-based negative electrode coating slurry more stable.

[0079] Furthermore, the thickener is one or more of ethyl cellulose or modified cellulose. Modified cellulose, such as highly substituted hydroxypropyl cellulose, ethyl cellulose, and highly substituted hydroxypropyl cellulose, are all soluble in ethanol, which increases the viscosity of the aqueous negative electrode coating slurry, thereby controlling the viscosity of the aqueous negative electrode coating slurry and making it easier to coat the aqueous negative electrode coating slurry onto the surface of the base film.

[0080] In one embodiment, the negative electrode binder is modified polyvinylidene fluoride (PVDF), and the negative electrode coating dispersant is one or two of polyethylene glycol, hexadecylbenzene sulfonic acid, and modified polyacrylic acid. In this embodiment, PVDF is modified to add hydrophilic groups, thereby introducing hydrophilic groups into the modified PVDF. These hydrophilic groups are polar, making the modified PVDF miscible in polar ethanol. In this embodiment, the negative electrode coating dispersant is soluble in ethanol solvent. The negative electrode coating dispersant can increase the surface activity of particles or powders, effectively preventing them from precipitating or agglomerating in the liquid, improving the wettability between aerogels, and thus allowing the negative electrode binder and aerogel additive to be uniformly dispersed in ethanol, thereby forming a stable suspension or emulsion state of aqueous negative electrode coating slurry.

[0081] Further, in one embodiment, the solid content of the oil-based positive electrode coating slurry is 10%-45%, and the solid content of the water-based negative electrode coating slurry is 15%-45%. In this embodiment, when the solid content of the oil-based positive electrode coating slurry is less than 15%, the content of polyvinylidene fluoride (PVDF) is too low, resulting in a thin coating and insufficient adhesion between PVDF and the positive and negative electrode sheets, which easily leads to detachment. When the solid content of the oil-based positive electrode coating slurry is greater than 45%, the thickness of the oil-based positive electrode coating slurry is thicker, thereby increasing the thickness between the positive electrode sheet, the separator, and the negative electrode sheet, thus reducing the energy density of the battery. When the solid content of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry is between 15% and 45%, the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry contain sufficient PVDF, thereby enabling the oil-based positive electrode coating and the water-based negative electrode coating to effectively bond the positive electrode sheet, the base film, and the negative electrode sheet together.

[0082] Furthermore, in this embodiment, different amounts of aerogel additive in the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry will result in different porosities in the oil-based positive electrode coating and the water-based negative electrode coating. Therefore, the proportion of aerogel additive added to the oil-based positive electrode coating slurry is the same as that added to the water-based negative electrode coating to ensure that the porosities in the oil-based positive electrode coating and the water-based negative electrode coating are the same. When the oil-based positive electrode coating and the water-based negative electrode coating are immersed in electrolyte, the electrolyte capacity immersed on the positive and negative electrode sheets is the same.

[0083] Furthermore, when the proportion of aerogel additive added in the preparation of the oily positive electrode coating slurry is the same as that added in the aqueous negative electrode coating, the positive electrode coating binder in the oily positive electrode coating slurry and the thickener and negative electrode coating binder in the aqueous negative electrode coating slurry result in different solid contents between the oily positive electrode coating slurry and the aqueous negative electrode coating slurry. This leads to a deviation in the aerogel additives used in the oily positive electrode coating and the aqueous negative electrode coating formed after drying. Therefore, after adding aerogel additives to the intermediate negative electrode slurry and stirring and dispersing for 120-150 minutes to obtain the aqueous negative electrode coating slurry, the solid content of the aqueous negative electrode coating slurry is adjusted, including the following steps:

[0084] The oily positive electrode coating slurry was sampled and baked to obtain the solid content of the oily positive electrode coating slurry, and the watery negative electrode coating slurry was sampled and baked to obtain the solid content of the watery negative electrode coating slurry.

[0085] When the solid content of the oily positive electrode coating slurry is greater than that of the watery negative electrode coating slurry by 0.5%, the watery negative electrode coating slurry is adjusted by adding 1% of modified polyvinylidene fluoride powder and mixing to increase the solid content of the prepared watery negative electrode coating slurry.

[0086] When the solid content of the oily positive electrode coating slurry is greater than the solid content of the watery negative electrode coating slurry by 0.5%, the watery negative electrode coating slurry is adjusted by adding 2% ethanol and mixing to reduce the solid content of the prepared watery negative electrode coating slurry.

[0087] In this embodiment, by adjusting the solid content of the aqueous negative electrode coating slurry, the thickness difference between the oily positive electrode coating formed after the oily positive electrode coating slurry is dried and the aqueous negative electrode coating formed after the aqueous negative electrode coating slurry is dried is reduced. This reduces the deviation in the distribution of aerogel additives in the oily positive electrode coating and the aqueous negative electrode coating, thereby ensuring that the electrolyte content on both sides of the lithium-ion separator remains consistent.

[0088] In one embodiment, the aerogel additive includes organic aerogels and inorganic aerogels, wherein the inorganic aerogel is at least one of SiO2 aerogel and Al2O3 aerogel; and the organic aerogel is at least one of polyurea aerogel and polyimide aerogel. In this embodiment, the SiO2 aerogel and Al2O3 aerogel have high-temperature resistance, which makes them have strong heat resistance in the subsequent PVDF pressing process, preventing breakage during hot pressing. This makes the SiO2 aerogel and Al2O3 aerogel in the formed oily positive electrode coating slurry and watery negative electrode coating slurry less prone to damage, and improves the heat resistance of the oily positive electrode coating and watery negative electrode coating. Polyurea aerogel and polyimide aerogel have the characteristics of high mechanical properties, good thermal stability, and extremely low thermal conductivity. Polyurea aerogel and polyimide aerogel can improve the resistance to heat shrinkage. When the lithium-ion separator is hot-pressed with the positive and negative electrode sheets, the good heat resistance of SiO2 aerogel, Al2O3 aerogel, polyurea aerogel and polyimide aerogel makes their structure less prone to breakage, resulting in the lithium-ion separator having good electrolyte absorption capacity and resistance to heat shrinkage.

[0089] Furthermore, the inorganic aerogel also includes at least one of carbon nanotube aerogel and graphene aerogel. Carbon nanotube aerogel and graphene aerogel have good conductivity and can form a conductive network on the membrane surface, promoting electron transport and thus reducing the interfacial reaction resistance of the battery. The organic aerogel also includes at least one of polyurethane aerogel, polybenzoxazine aerogel, syndiotactic polystyrene aerogel, polym-phenylenediamine aerogel, polyamide aerogel, polyvinylidene fluoride aerogel, and polypyrrole aerogel. These organic aerogels improve the electrolyte absorption performance of the lithium-ion membrane.

[0090] Furthermore, in one embodiment, when the added organic aerogel is hydrophobic, such as the strong hydrophobicity of polyurea aerogel, the dispersion and wetting effect of polyurea aerogel in the aqueous negative electrode coating slurry is poor. Before adding the aerogel additive and stirring for 120-150 minutes, and after stirring the added negative electrode coating dispersant for 60-120 minutes, the wetting agent hexadecylbenzenesulfonic acid is also added. In this embodiment, hexadecylbenzenesulfonic acid reduces the surface tension of the polyurea aerogel, thereby allowing the solvent ethanol to wet the polyurea aerogel, avoiding uneven distribution of the polyurea aerogel, which would lead to uneven pore distribution in the obtained lithium-ion membrane aqueous positive electrode coating. This ensures that the polyurea aerogel is dispersed in the aqueous positive electrode coating slurry, giving the aqueous positive electrode coating good electrolyte wetting and high-temperature heat shrinkage resistance.

[0091] In one embodiment, the organic aerogel component in the aerogel additive is 20%-80% by mass, and the inorganic aerogel component in the aerogel additive is 20%-80% by mass. In this embodiment, the organic aerogel has good electrolyte absorption capacity and high mechanical strength, while the inorganic aerogel has good heat resistance and shrinkage resistance. The inorganic aerogel in the aerogel additive has good heat resistance. When the proportion of inorganic aerogel in the aerogel additive is relatively high, the heat resistance of the lithium-ion separator is better during the hot pressing process with the positive and negative electrode sheets, thereby reducing the damage of both organic and inorganic aerogels.

[0092] In one embodiment, the thickness of the base film is 5μm-20μm, the thickness of the oil-based positive electrode coating slurry is 1μm-5μm, and the thickness of the water-based negative electrode coating slurry is 1μm-5μm. In this embodiment, oil-based positive electrode coating slurry and water-based negative electrode coating slurry of the same thickness can be coated on both sides of the base film. The base film can provide good support strength and insulation performance. After drying, the oil-based positive electrode coating slurry can form a coating with a thickness of 1μm-5μm, allowing the oil-based positive electrode coating to accommodate a certain amount of electrolyte. After drying, the water-based negative electrode coating slurry can also form a coating with a thickness of 1μm-5μm, allowing the water-based negative electrode coating to accommodate a certain amount of electrolyte. This also improves the high-temperature heat shrinkage resistance of the lithium-ion separator.

[0093] Furthermore, when the coating thicknesses of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry differ, the adhesion between the lithium-ion separator and the positive and negative electrode sheets will also differ. Controlling the coating thicknesses of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry controls the thickness of the dried oil-based positive electrode coating and the water-based negative electrode coating. It can be understood that the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry are coated separately using a double-sided coating device, controlling the areal density of the two dies. The coating orifice sizes of the two dies are the same, and by controlling the viscosity of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry to be the same, the coating of the two dies can be controlled to coat the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry with similar thicknesses onto both sides of the base film. Therefore, after preparing the water-based negative electrode coating slurry, the viscosity of the water-based negative electrode coating slurry is adjusted, including the following steps:

[0094] The viscosity of the water-based negative electrode coating slurry and the viscosity of the oil-based positive electrode coating slurry were tested and compared.

[0095] If the viscosity of the aqueous negative electrode coating slurry is less than that of the oil-based positive electrode coating slurry, increase the viscosity of the aqueous negative electrode coating slurry. Add 0.1% ethyl cellulose (by mass of the total aqueous negative electrode coating slurry) to the aqueous negative electrode coating slurry and stir to disperse. Then test the viscosity of the adjusted aqueous negative electrode coating slurry. Repeat the test and comparison of the viscosity of the aqueous negative electrode coating slurry and the viscosity of the oil-based positive electrode coating slurry.

[0096] If the viscosity of the aqueous negative electrode coating slurry is less than that of the oil-based positive electrode coating slurry, add 0.1% polyacrylate (by mass of the total oil-based positive electrode coating slurry) to the oil-based positive electrode coating slurry and stir to disperse. Then test the viscosity of the adjusted oil-based positive electrode coating slurry. Repeat the test and comparison of the viscosity of the aqueous negative electrode coating slurry and the oil-based positive electrode coating slurry.

[0097] In this embodiment, by controlling the viscosity of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry to be the same, the coating of the two dies allows the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry of similar thickness to be coated on both sides of the base film. The similar thickness of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry results in a similar thickness of the oil-based positive electrode coating after drying, and similar porosity of the oil-based positive electrode coating and the water-based negative electrode coating slurry on both sides of the lithium-ion separator. The similar adhesion between the lithium-ion separator and the positive and negative electrode sheets results in better uniformity among the positive electrode sheet, the lithium-ion separator, and the negative electrode sheet, thus avoiding wrinkles in the lithium-ion separator.

[0098] In one embodiment, when preparing the oil-based positive electrode coating slurry or the water-based negative electrode coating slurry, 1%-5% of ammonium bicarbonate, a pore-forming agent, may be added to the total amount of the coating slurry. In this embodiment, the ammonium bicarbonate decomposes during the baking process of the oil-based positive electrode coating slurry or the water-based negative electrode coating slurry, increasing the specific surface area of ​​the formed pore structure, thereby reducing the resistance and improving the diffusion of the electrolyte, allowing the electrolyte to wet the oil-based positive electrode coating or the water-based negative electrode more quickly.

[0099] The application also provides a lithium-ion separator, prepared using the lithium-ion separator preparation method described above. In this embodiment, an oil-based positive electrode coating slurry and an aqueous negative electrode coating slurry are respectively coated on both sides of a base film and dried to form a lithium-ion separator in which an oil-based positive electrode coating, a base film, and an aqueous negative electrode coating are sequentially stacked.

[0100] This application also provides a method for preparing a lithium-ion battery, characterized in that it includes a lithium-ion separator obtained by the method for preparing a lithium-ion separator as described in any of the above embodiments.

[0101] A positive electrode sheet, a lithium-ion separator, and a negative electrode sheet are wound together to form a core, and the core is hot-pressed to obtain a battery cell.

[0102] The hot-pressed battery cells are installed in the battery casing, and then liquid-filled formation is performed to obtain the lithium-ion battery.

[0103] In this embodiment, hot pressing causes the polyvinylidene fluoride (PDVF) in the oily positive electrode coating of the lithium-ion separator to come into contact with the positive electrode sheet after being heated, thus ensuring that the positive electrode sheet and the oily positive electrode coating are fully bonded together. Similarly, hot pressing causes the polyvinylidene fluoride (PDVF) in the watery negative electrode coating of the lithium-ion separator to come into contact with the negative electrode sheet after being heated, thus ensuring that the negative electrode sheet and the watery positive electrode coating are fully bonded together.

[0104] In one embodiment, the hot-pressing process uses a pressure of 0.05 MPa to 1 MPa, and the holding time is 3 to 6 hours. In this embodiment, excessive pressure on organic and inorganic aerogels can easily cause breakage, thereby compromising their effectiveness in the oil-based positive electrode coating and the water-based negative electrode coating. A hot-pressing pressure of 0.05 MPa to 1 MPa ensures lower pressure between the positive electrode sheet and the lithium-ion separator and negative electrode sheet, preventing the aerogel additives from being damaged and losing their effectiveness. The holding time of 3 to 6 hours ensures tight adhesion between the positive electrode sheet, the lithium-ion separator, and the negative electrode sheet, reducing gaps between them and preventing wrinkles in the lithium-ion separator.

[0105] Furthermore, the hot-pressing process temperature is 45℃~85℃. Therefore, when the core is hot-pressed, the temperature needs to be controlled at 85℃. When the hot-pressing process temperature is below 45℃, the PDVF (polyvinylidene fluoride) melts poorly, the adhesion between the oil-based positive electrode coating and the positive electrode sheet is poor, and the adhesion between the water-based negative electrode coating and the negative electrode sheet is poor. This results in air remaining between the lithium-ion separator and the positive and negative electrode sheets, causing the lithium-ion separator to easily wrinkle, thus affecting the performance of the lithium-ion battery. When the hot-pressing process temperature is above 85℃, the PDVF melts better, but when organic and inorganic aerogels are pressurized and heated to a higher temperature, the organic and inorganic aerogels... The porous structure of organic aerogels is easily damaged, which leads to the destruction of organic and inorganic aerogels in the oil-based positive electrode coating and the water-based negative electrode coating. This reduces the electrolyte wetting effect and the resistance to high-temperature heat shrinkage in the lithium-ion separator. When the hot pressing process temperature is 45-85℃, the polyvinylidene fluoride (PDVF) melts better, resulting in better adhesion between the oil-based positive electrode coating and the positive electrode sheet, and better adhesion between the water-based negative electrode coating and the negative electrode sheet. The porous structure of the organic and inorganic aerogels in the lithium-ion separator remains intact, thereby improving the electrolyte wetting effect and the resistance to high-temperature heat shrinkage in the lithium-ion separator.

[0106] Compared with the prior art, this disclosure has at least the following advantages:

[0107] 1. The above-mentioned method for preparing lithium-ion separators utilizes the porous network structure of aerogel additives to create a large number of pores between the oily positive electrode coating and the watery negative electrode coating, thereby improving the wetting effect of the electrolyte. The porous network structure of the aerogel additives also improves the high-temperature thermal shrinkage resistance of the lithium-ion separator and reduces the internal resistance of the battery.

[0108] 2. The oil-based positive electrode coating slurry uses an oil-based solvent. The oil-based positive electrode coating slurry is similar to the oil-based system of the positive electrode coating, which improves the adhesion performance between the oil-based positive electrode coating and the positive electrode. The water-based negative electrode coating slurry uses a water-based solvent coating. The water-based negative electrode coating slurry is similar to the water-based system of the negative electrode coating, which improves the adhesion performance between the water-based negative electrode coating and the negative electrode. This avoids the presence of gaps between the lithium-ion separator and the positive and negative electrodes, which would cause wrinkles in the lithium-ion separator. As a result, the lithium battery produced has better consistency and cycle stability.

[0109] 3. The oil-based positive electrode coating slurry uses methyl ethyl ketone (MEK) as the solvent, while the water-based negative electrode coating slurry uses ethanol. Both MEK and ethanol are low-boiling-point solvents, which makes the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry easy to volatilize during the baking process, avoiding solvent residue on the lithium-ion separator. The boiling points of MEK and ethanol are close, which makes the drying time of the oil-based positive electrode coating slurry and the water-based negative electrode coating slurry similar, thereby making the formed lithium-ion separator more uniform and resulting in better consistency of the battery made from the lithium-ion separator.

[0110] The following are some specific examples. Where %, it refers to a percentage by weight. It should be noted that the following examples do not exhaustively cover all possible scenarios, and unless otherwise specified, the materials used in the following examples are commercially available.

[0111] Example 1

[0112] First, add 0.5% dispersant and 5% ethyl cellulose thickener to ethanol and stir until homogeneous. Then, slowly add 10% modified PVDF powder and set the kneader speed to 1000 rpm. Then, grind and disperse the mixture through kneading for 60 minutes to ensure uniform mixing. Next, add 10% silica aerogel and 10% polyurea aerogel and stir until homogeneous. Stir for 120 minutes at a speed of 1500 rpm to obtain the water-based negative electrode coating slurry.

[0113] Then, 0.5% dispersant, 5% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 10% polyvinylidene fluoride (PVDF) powder were added to methyl ethyl ketone (MEK). The kneader was set to 1000 rpm and kneaded for 60 minutes to ensure uniform mixing and obtain an oily positive electrode coating slurry.

[0114] Oily positive electrode coating slurry and watery negative electrode coating slurry were respectively coated on a base film with a thickness of 5-20 μm and a porosity of 20-70% at a coating speed of 25 m / min to obtain a transition coating membrane with a thickness of 3 μm for the oily positive electrode coating slurry coating and a thickness of 3 μm for the watery negative electrode coating slurry coating; then the transition coating membrane was dried in an oven at a temperature of 30-60℃ to obtain the lithium-ion membrane of Example 1.

[0115] Example 2

[0116] First, add 0.5% dispersant and 5% ethyl cellulose thickener to ethanol and stir evenly. Then, slowly add 10% modified PVDF powder. Set the kneader speed to 1000 rpm and then process and grind the mixture for 60 minutes to make the slurry evenly mixed, thus obtaining the water-based negative electrode coating slurry.

[0117] Then, 0.5% dispersant, 5% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 10% polyvinylidene fluoride (PVDF) powder were added to methyl ethyl ketone (MEK). The kneader was set to 1000 rpm and kneaded for 60 minutes to ensure uniform mixing. Then, 10% silica aerogel and 10% polyurea aerogel were added and stirred to ensure uniform mixing for 120 minutes at 1500 rpm to obtain an oily positive electrode coating slurry.

[0118] Oily positive electrode coating slurry and watery negative electrode coating slurry were respectively coated on a base film with a thickness of 5-20 μm and a porosity of 20-70% at a coating speed of 25 m / min to obtain a transition coating membrane with a thickness of 3 μm for the oily positive electrode coating slurry coating and a thickness of 3 μm for the watery negative electrode coating slurry coating; then the transition coating membrane was dried in an oven at a temperature of 30-60℃ to obtain the lithium-ion membrane of Example 2.

[0119] Example 3

[0120] First, add 0.5% dispersant and 5% ethyl cellulose thickener to ethanol and stir evenly. Then, slowly add 10% modified PVDF powder and set the kneader speed to 1000 rpm. Then, grind and disperse the mixture through kneading for 60 minutes to make the slurry evenly mixed. Add 10% silica aerogel and 10% polyurea aerogel to the mixture and stir to make it evenly mixed. Stir for 120 minutes at a speed of 1500 rpm to obtain the water-based negative electrode coating slurry.

[0121] Then, 0.5% dispersant, 5% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 10% polyvinylidene fluoride (PVDF) powder were added to methyl ethyl ketone (MEK). The kneader was set to 1000 rpm and kneaded for 60 minutes to ensure uniform mixing. Then, 10% silica aerogel and 10% polyurea aerogel were added and stirred to ensure uniform mixing for 120 minutes at 1500 rpm to obtain an oily positive electrode coating slurry.

[0122] Oily positive electrode coating slurry and watery negative electrode coating slurry were respectively coated on a base film with a thickness of 5-20 μm and a porosity of 20-70% at a coating speed of 25 m / min to obtain a transition coating membrane with a thickness of 3 μm for the oily positive electrode coating slurry coating and a thickness of 3 μm for the watery negative electrode coating slurry coating; then the transition coating membrane was dried in an oven at a temperature of 30-60℃ to obtain the lithium-ion membrane of Example 3.

[0123] Example 4

[0124] First, add 0.5% dispersant and 5% ethyl cellulose thickener to ethanol and stir until homogeneous. Then, slowly add 10% modified PVDF powder, setting the kneader speed to 1000 rpm. Next, knead and disperse the mixture for 60 minutes to ensure uniform mixing. Then, add 10% silica aerogel and 10% poly(m-phenylene diamine) aerogel, stirring until homogeneous for 120 minutes at 1500 rpm to obtain the aqueous negative electrode coating slurry. Finally, add 5% ammonium bicarbonate to the aqueous negative electrode coating slurry and stir at 1000 rpm for 60 minutes.

[0125] Then, 0.5% dispersant, 5% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 10% polyvinylidene fluoride (PVDF) powder were added to methyl ethyl ketone (MEK). The kneader was set to 1000 rpm and kneaded for 60 minutes to ensure uniform mixing. Then, 10% silica aerogel and 10% polyurea aerogel were added and stirred to ensure uniform mixing for 120 minutes at 1500 rpm to obtain an oily positive electrode coating slurry.

[0126] Oily positive electrode coating slurry and watery negative electrode coating slurry were respectively coated on a base film with a thickness of 5-20 μm and a porosity of 20-70% at a coating speed of 25 m / min to obtain a transition coating membrane with a thickness of 3 μm for the oily positive electrode coating slurry coating and a thickness of 3 μm for the watery negative electrode coating slurry coating; then the transition coating membrane was dried in an oven at a temperature of 30-60℃ to obtain the lithium-ion membrane of Example 4.

[0127] Comparative Example 1

[0128] First, add 0.5% dispersant and 5% ethyl cellulose thickener to ethanol and stir evenly. Then, slowly add 10% modified PVDF powder and set the kneader speed to 1000 rpm. Then, grind and disperse the mixture through kneading for 60 minutes to make the slurry evenly mixed. Add 20% silica aerogel and stir to make it evenly mixed. Stir for 120 minutes at a speed of 1500 rpm to obtain the water-based negative electrode coating slurry.

[0129] Then, 0.5% dispersant, 5% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 10% polyvinylidene fluoride (PVDF) powder were added to methyl ethyl ketone (MEK). The kneader was set to 1000 rpm and kneaded for 60 minutes to ensure uniform mixing. 20% silica aerogel was then added and stirred for 120 minutes at 1500 rpm to obtain an oily positive electrode coating slurry.

[0130] Oily positive electrode coating slurry and watery negative electrode coating slurry were respectively coated on a base film with a thickness of 5-20 μm and a porosity of 20-70% at a coating speed of 50 m / min to obtain a transition coating membrane with a thickness of 3 μm for the oily positive electrode coating slurry coating and a thickness of 3 μm for the watery negative electrode coating slurry coating; then the transition coating membrane was dried in an oven at a temperature of 30-60℃ to obtain the lithium-ion separator of Example 1.

[0131] Comparative Example 2

[0132] First, 0.5% dispersant, 5% polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and 10% polyvinylidene fluoride (PVDF) powder were added to methyl ethyl ketone (MEK). The kneader was set to 1000 rpm, and then kneaded for 60 minutes to ensure uniform mixing. Then, 10% silica aerogel and 10% polyurea aerogel were added and stirred to ensure uniform mixing for 120 minutes at 1500 rpm to obtain the positive electrode oily coating slurry.

[0133] The coating slurry is applied to a base film with a thickness of 5-20 μm and a porosity of 20-70% at a coating speed of 50 m / min to obtain a coating with a thickness of 1-5 μm. Only one side is coated to obtain a transition coating membrane with an oily positive electrode coating slurry coating thickness of 3 μm. Then, the transition coating membrane is dried in an oven at a temperature of 30-60℃ to obtain the lithium-ion membrane of Comparative Example 2.

[0134] Comparative Example 3

[0135] First, add 0.5% dispersant and 5% ethyl cellulose thickener to ethanol and stir until homogeneous. Then, slowly add 10% modified PVDF powder and set the kneader speed to 1000 rpm. Then, grind and disperse the mixture through kneading for 60 minutes to ensure uniform mixing. Add 10% silica aerogel and 10% poly(m-phenylene diamine) aerogel and stir until homogeneous for 120 minutes at a speed of 1500 rpm to obtain the water-based negative electrode coating slurry.

[0136] The coating slurry is applied to a base film with a thickness of 5-20 μm and a porosity of 20-70% at a coating speed of 25 m / min to obtain a coating with a thickness of 1-5 μm. Only one side is coated to obtain a transition coating membrane with a thickness of 3 μm. The transition coating membrane is then dried in an oven at a temperature of 30-60℃ to obtain the lithium-ion membrane of Comparative Example 3.

[0137] Comparative Example 4

[0138] A conventional lithium-ion membrane of the same thickness as the prepared membrane was used without any treatment.

[0139] The prepared lithium-ion separator was tested by winding the oil-based positive electrode coating with the coated side facing the positive electrode sheet and the water-based negative electrode coating with the coated side facing the negative electrode sheet, followed by hot pressing to form a lithium-ion cell, and then injecting liquefaction to form a lithium-ion battery. The positive electrode material used in the positive electrode sheet is one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron phosphate, while the negative electrode sheet uses graphite as the negative electrode material. The lithium-ion battery was then subjected to performance tests, mainly including: cycle performance test, battery liquid retention, battery internal resistance, and battery capacity retention rate. Battery model: 986771-5800mAh, liquid retention 15.8g.

[0140] Table 1. Test Results of Comparative Examples and Embodiments

[0141]

[0142] Comparing Examples 1-4 with Comparative Example 4 in Table 1, the lithium batteries prepared by adding aerogel additives to the lithium-ion separator showed improved electrolyte retention, internal resistance, and capacity retention after 500 cycles. This indicates that the lithium batteries prepared by adding aerogel additives to the lithium-ion separator have increased absorption and wetting performance of the electrolyte, and improved resistance to thermal shrinkage.

[0143] Comparing Example 3 and Example 4, the addition of ammonium bicarbonate pore-forming agent helps to reduce the internal resistance of the battery;

[0144] Comparing Example 3 with Comparative Example 1, the electrolyte retention of lithium batteries made with only inorganic aerogel as the aerogel additive is lower than that of lithium batteries made with both inorganic and organic aerogel as the aerogel additive. This indicates that organic aerogel has a stronger ability to absorb electrolyte, thereby improving the performance of lithium batteries.

[0145] Comparing Example 1 and Comparative Example 2, the lithium battery without an oil-based positive electrode coating on the lithium-ion separator exhibits lower liquid retention, internal resistance, and capacity retention after 500 cycles, but higher full-charge expansion rate compared to the lithium battery with an oil-based positive electrode coating. Similarly, comparing Example 2 and Comparative Example 3, the lithium battery without an aqueous negative electrode coating on the lithium-ion separator exhibits lower liquid retention, internal resistance, and capacity retention after 500 cycles, but higher full-charge expansion rate compared to the lithium battery with an aqueous negative electrode coating. This indicates that the double-layer structure of the lithium-ion separator, with an oil-based positive electrode coating and an aqueous negative electrode coating on both sides, improves the wetting ability during electrolysis and enhances the lithium-ion exchange capacity between the lithium-ion separator and the positive and negative electrode plates.

[0146] Comparing the positive electrode side peelability of the positive electrode sheet and oily positive electrode coating with the negative electrode side peelability of the negative electrode sheet and aqueous negative electrode coating in Examples 1 and 2, the adhesion performance of the aqueous negative electrode coating in Example 1, which added 10% silica aerogel and 10% polyurea aerogel, decreased, as did the adhesion performance of the oily positive electrode coating in Example 2, which also added 10% silica aerogel and 10% polyurea aerogel. This indicates that the addition of aerogel additives affected the adhesion performance of both the oily positive electrode coating and the aqueous negative electrode coating.

[0147] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing a lithium-ion separator, characterized in that, Includes the following steps: An oily positive electrode coating slurry is prepared, wherein the oily positive electrode coating slurry contains an aerogel additive, and the solvent of the oily positive electrode coating slurry is methyl ethyl ketone (MEK). An aqueous negative electrode coating slurry is prepared, wherein the aqueous negative electrode coating slurry contains an aerogel additive, and the solvent of the aqueous negative electrode coating slurry is ethanol; The oily positive electrode coating slurry is coated on one side of the base membrane, and the watery negative electrode coating slurry is coated on the other side of the base membrane to obtain a transition-coated separator. The transition-coated separator is dried to remove methyl ethyl ketone and ethanol, thereby obtaining a lithium-ion separator in which an oily positive electrode coating, a base film, and an aqueous negative electrode coating are sequentially arranged. The transition coating separator is dried at a temperature of 30℃-60℃ for 0.5h-3h. A double-sided coating device is used to coat both sides of the base membrane simultaneously. The transition coating separator is then dried in a floating drying oven to dry the oily positive electrode coating slurry and the watery negative electrode coating slurry on both sides of the base membrane, so that the oily positive electrode coating and the watery negative electrode coating are formed on both sides of the transition coating separator, respectively.

2. The method for preparing a lithium-ion separator according to claim 1, characterized in that, The preparation of the oily positive electrode coating slurry includes the following steps: Add the positive electrode coating binder to methyl ethyl ketone (MEK), then add the positive electrode coating dispersant and stir for 60-120 minutes to obtain the positive electrode intermediate slurry. The positive electrode intermediate slurry is added with an aerogel additive and stirred and dispersed for 120-150 minutes to obtain an oily positive electrode coating slurry. The oily positive electrode coating slurry comprises the following components by weight: Positive electrode coating binder: 15%-30%; Butyl ketone: 44.5%-79.5%; Positive electrode coating dispersant: 0.5%; Aerogel additives: 5%-25%.

3. The method for preparing a lithium-ion separator according to claim 2, characterized in that, The positive electrode coating binder is at least one of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); the positive electrode coating dispersant is at least one of polyethylene glycol, hexadecylbenzene sulfonic acid, and modified polyacrylic acid.

4. The method for preparing a lithium-ion separator according to claim 1, characterized in that, The preparation of the aqueous negative electrode coating slurry includes the following steps: Add the negative electrode binder and thickener to ethanol, then add the negative electrode coating dispersant, and grind and disperse for 60 min-120 min to obtain the negative electrode intermediate slurry; Aerogel additives are added to the negative electrode intermediate slurry and stirred and dispersed for 120-150 minutes to obtain an aqueous negative electrode coating slurry. The aqueous negative electrode coating slurry comprises the following components by mass: Negative electrode binder: 10%-20%; Thickener: 5%-10%; Ethanol: 44.5%-79.5%; Negative electrode coating dispersant: 0.5%; Aerogel additives: 5%-25%.

5. The method for preparing the lithium-ion separator according to claim 4, characterized in that, The negative electrode binder is modified polyvinylidene fluoride; the negative electrode coating dispersant is at least one of polyethylene glycol, hexadecylbenzene sulfonic acid, and modified polyacrylic acid.

6. The method for preparing a lithium-ion separator according to claim 1, characterized in that, The aerogel additive includes organic aerogels and inorganic aerogels, wherein the inorganic aerogel is at least one of SiO2 aerogel and Al2O3 aerogel; and the organic aerogel is at least one of polyurea aerogel and polyimide aerogel.

7. The method for preparing a lithium-ion separator according to claim 1, characterized in that, The thickness of the base film is 5μm-20μm, the thickness of the oil-based positive electrode coating is 1μm-5μm, and the thickness of the water-based negative electrode coating is 1μm-5μm.

8. A lithium-ion separator, characterized in that, The lithium-ion separator was prepared using the method described in any one of claims 1 to 7.

9. A method for preparing a lithium-ion battery, characterized in that, This includes lithium-ion separators obtained using the preparation method of lithium-ion separators according to any one of claims 1 to 7. A positive electrode sheet, a lithium-ion separator, and a negative electrode sheet are wound together to form a core, and the core is hot-pressed to obtain a battery cell. The hot-pressed battery cells are installed in the battery casing, and then liquid-filled formation is performed to obtain the lithium-ion battery.

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